I think Marvel's independance has been a huge success. This in-house deal has to do with profit, not with control of their characters. They got shafted by Sony with all the money the Spider-man movies made. They even had to take Sony to court, because they were marketing Spider-man without their permission.
Also it's incorrect to say the studio now owns the characters. Marvel owns the rights to all their characters and will always retain those rights. Sony, Fox, Universal only own the rights to the movie versions of the character for a said amount of time. With Universal their movie rights to the Hulk are null and void, and Marvel can now market the Hulk to any studio they want.
Warner has been a huge problem for DC and always has been. The Donner Superman movies were done as a negative pickup, which means the entire financing of the film was handled independantly of Warner Brothers.
DC still cannot sell the studio on other projects like Green Lantern, Flash and Wonder Woman, that would probably be huge hits with the fan base.
Superman Returns was a huge dissapointment for the big return of DC's flagship character. Whatever you feel about the movie personally, the movie was not broadly accepted. If you're going to blame Fox and Sony for decisions about the Green Goblin and Dr. Doom, then who is to blame for making Superman an illegitimate dad?
Not all Marvel project have been a success, and some have been just plain awful (Elektra), however Marvel has been more successful than DC of getting their projects out.